Lithium tetraborate, Li.sub.2 B.sub.4 O.sub.7, is an insulating dielectric material that is piezoelectric but is not ferroelectric. This means that it is capable of being mechanically stimulated into vibration (piezoelectric effect) but it is not necessary to subject the material to poling such as would be required for a ferroelectric material such as lithium niobate (LiNbO.sub.3) Furthermore, Li.sub.2 B.sub.4 O.sub.7 is not enantiomorphous. This means that it does not have the disadvantage of twinning as quartz does. Li.sub.2 B.sub.4 O.sub.7 has moderate piezoelectric coupling and orientations at which the first order temperature coefficient of frequency is zero.
Notwithstanding the presence of zero first-order temperature coefficient cuts, the resulting frequency versus temperature characteristics of resonators made from plates of Li.sub.2 B.sub.4 O.sub.7 cut at these orientations, is poor. This is because the second-order temperature coefficient of frequency is, in general, large at these orientations rendering them unsuitable as commercial resonators or transducers.
Most of the resonators or transducers in use today that have low temperature coefficients of frequency operate by virtue of the mechanical shear mode. The use of the thickness extensional mode of a plate has the advantage of a higher sound velocity than the shear waves thus giving a higher operating frequency for a given thickness. Moreover, in transducer applications, particularly, the extensional mode is preferred because it is more readily transmitted into other media.